1. Field of the Invention
The invention relates to labels. More specifically it relates to tire labels with RFID tags.
2. Description of the Related Art
Most tire labels whether they are tread labels or smart labels with RFID inserts are made from solid label films extruded from polymers such as polypropylene, polyethylene, polyvinyl chloride (vinyl), polyolefins and copolymer blends. The problem with these solid films is they can be stiff and non-conformable. Continuous exposure to ultraviolet radiation (sunlight) and high/low temperature extremes (thermal cycling) breaks down the film, resulting in loss of tensile strength, cracking, crazing, staining, and discoloration. Loss of plasticizers within the film also leads to a reduction in flexibility and conformability, as the label becomes hard and brittle.
The use of multi-layer films, primers, barrier layers and adhesive constructions is sometimes used to resist migration of mobile ingredients such as oils, resins, tackifiers, or plasticizers from within the rubber based adhesive layer that exhibit a high affinity for polyolefin face stocks. This migration of mobile ingredients into the label film often manifests itself as swelling or hardening of the label face stock which, in turn, leads to wrinkling of the label constructions and general loss of adhesion.
Barrier films and primer layers are sometimes used between the back of the label film and adhesive layer to prevent discoloration and loss of adhesion caused by migration of low molecular weight mobile components such as waxes, extender oils, lubricants, anti-reversion coagents, sulphide resins, and plasticized sulfur from within the tire into the label face stock and adhesive as the tire ages. This diffusion process can be restricted or influenced by several factors such as ambient temperature, humidity, concentration of filler contaminants in the rubber tire compound, the chemical make up of the label face stock, the chemical make up of the pressure sensitive adhesive, the thickness of the label face stock, and the thickness of the adhesive. Higher ambient temperature and humidity levels generally accelerate the diffusion process. Thus, it is desirable to have a label construction that restricts or prevents this diffusion process.
Typical tire labels may utilize multi-layer face stocks in combination with barrier layers, but the additional processing steps and curing of barrier components can make these constructions expensive to manufacture. To prevent diffusion of mobile low molecular weight components into the adhesive and label face stock the barrier layer must be designed to meet one or both of the following conditions:
The barrier layer must be comprised of a material that is dissimilar in terms of polarity. Since diffusion is promoted with materials of like chemistry, a dissimilar material will inhibit diffusion. For example, a non-polar material such as oil will not diffuse well through a solid polar film such as polyester (PET).
The barrier layer is comprised of a polymeric material that has specific structure such that migration of low molecular weight materials is restricted due to size exclusion. A highly branched polymer such as a solid polyester film may prevent component migration.
The problem with solid polyester film is high stiffness. This type of label film is not suitable for labeling a tire surface because it is not flexible and does not conform well to surface irregularities such as raised lettering, serrations, vent ports, and deep tread patterns. High stiffness prevents a good adhesive bond to build between the label and tire surface, thus, the PET label is likely to lift and fall off or catch on something and peel away.